1. Technical Field
The present disclosure relates to electrode active materials used in rechargeable lithium ion batteries and, particularly, to an electrode composite material, a method for making the same, and a rechargeable lithium ion battery using the same.
2. Description of Related Art
A common method to improve the properties of cathode active materials of lithium batteries is to treat the surface of the materials. For example, compared to untreated LiFePO4, the carbon coated LiFePO4 particles has improved conductivity. In another example, research has shown that composite material having AlPO4 coated LiCoO2 has a relatively high thermodynamic stability.
The method for forming the composite material includes preparing an amount of dispersed small AlPO4 particles in water, adding large LiCoO2 particles in the water having the small AlPO4 particles. The small AlPO4 particles adhere to the surface of the large LiCoO2 particles. The water is then evaporated and the LiCoO2 particles with the AlPO4 particles absorbed thereon are heated at about 700° C. to form the composite material.
However, AlPO4 is insoluble in water. Therefore, in the above method, small AlPO4 particles may not disperse sufficiently in the water and could aggregate together. Further, when a large amount of the LiCoO2 particles is added in the water, the LiCoO2 particles added earlier in time will absorb the majority of the AlPO4 particles in the water, and the subsequently added LiCoO2 particles may not have enough AlPO4 particles to absorb. The uneven absorption occurs most often when adding a relatively large amount of LiCoO2 particles, which is a problem for industrialization of this composite material. Furthermore, even though it may appear that the LiCoO2 is coated well, a microscopic view of the AlPO4 may show that the small particles coated on the surface of the LiCoO2 large particle do not form a uniform AlPO4 substance layer. Accordingly, the lithium ion battery using the composite material formed by the above method in the cathode electrode has a low cycling stability, especially in industry use.
What is needed, therefore, is to provide an electrode composite material having a uniform protective layer coated on the electrode active materials, a method for making the same, and a lithium ion battery using the same.